The major urinary metabolite of the pineal hormone melatonin, 6-hydroxymelatonin is being quantified by gas chromatography-negative chemical ionization mass spectrometry. Urinary excretion rates of this metabolite are being used to determine the possible role of the pineal gland in human reproductive biology - i.e., its function during pubertal development and throughout the menstrual cycle. A longitudinal study of melatonin metabolite excretion by young girls is in the fourth year. Each girl has maintained a self-consistent level of excretion, which has not, as yet, correlated with pubertal change. Collaborative studies on transplantation of neonatal rat pineals into pinealectomized rats have begun utilizing the assay of urinary 6-hydroxymelatonin as a measure of pineal function (day and night). Collaborative clinical studies on effects of tricyclic antipressants and aging are in progress.